Bike advocates are always pushing for more infrastructure and most agree that having designated bike lanes separate from car lanes generally eases some of the tensions.

That is, until a car double parks in one of those lanes or drives through it, forcing a cyclist to stop or ride on the sidewalk -- which is illegal -- or enter traffic, which can be dangerous to the person on the bike and those in cars trying to get around the cyclist.

BikeDenver, the city's main advocacy group for cyclists, has asked its supporters to keep an eye out for illegally parked cars taking up these lanes and to send over photos. The group has shared some of them with us, and we've also snapped a few of our own around town.

But first -- what is the law here?

Emily Williams, a spokeswoman for the city's Public Works Department, writes to us:

Overall, cars parking in bike lanes is one of those growing pains Denver is experiencing as we continue to evolve into a more multimodal city; it is important for all commuters to be aware of their surroundings. A bike lane is considered part of the travel lane, therefore Denver Police has the authority to cite the offending driver. Parking in a bike lane is illegal and it is important that drivers understand that where they park can affect the transportation system as a whole.

Piep van Heuven, executive director of BikeDenver, says, "We are focused on this as a safety issue. It's not just a safety issue for bicycles, but it's a safety issue for everybody. If a cyclist has to leave a bike lane...nobody's where they are supposed to be and it really is unsafe for everyone."

Van Heuven says that in general, there needs to be more education around bike lanes so that drivers and cyclists know how they are supposed to be used.

"I think some people don't understand that a bike lane is a vehicle lane," she says, adding, "You wouldn't just park a truck in the middle of a car lane."

Cyclists sometimes ride in bike lanes the wrong direction and that's also very problematic, she adds.

"There's a whole variety of...habits happening in bike lanes that are not good for everybody," she says. "What we're trying to get at is a bike lane is a vehicle lane."

Continue for more photos of cars in Denver's bike lanes.

A dozen cars all blocking the 14th Street bike lane during the Great American Beer Festival earlier this year.

Courtesy of BikeDenver

What appears to be a city vehicle parked in a bike lane on Arapahoe.

Courtesy of BikeDenver

Car double parked in a bike lane on 16th Avenue.

Sam Levin

Continue for more photos.

Car blocking bike lane in Montview.

Courtesy of BikeDenver

Sign blocking a bike lane downtown.

Courtesy of BikeDenver

A UPS truck blocking bike lane on Wynkoop.

Courtesy of BikeDenver

Continue for more photos.

A car with "Share the Road" plates blocking a bike lane.

Courtesy of BikeDenver

A police car blocking a bike lane on Bannock, in front of the City and County building.